Circuit arrangements such as are used in smart cards, for example, can be exposed to attacks. In order to avert such attacks, countermeasures are usually provided which are triggered after detection of an attack. Said countermeasures are intended at least to make it more difficult to spy out data or the functioning of the circuit arrangement.
In order to identify an attack it is possible to use analog sensors, for example, which detect an alteration of the operating conditions. Such sensors can be embodied as a voltage sensor, frequency sensor, temperature sensor or light sensor. If the measured value exceeds a predetermined threshold value, an alarm is triggered, as a consequence of which the countermeasures are initiated.
In order to check the functionality of the sensors, it is possible to use a so-called “Usermode Sensor Life Control”, abbreviated to “UmSLC”. During a test, the sensors are adjusted or stimulated by the UmSLC in such a way that an alarm is triggered. In test operation, however, normally no countermeasures are initiated in reaction to said alarm, rather a check is merely made to determine whether the alarm is generated after adjustment or stimulation of the sensor. If the alarm fails to occur, this allows the conclusion to be drawn of an attack in which the sensor has been manipulated or deactivated. This procedure serves as a functional test of circuit arrangements with analog sensors. The conventional UmSLC, oriented to testing analog sensors, cannot be used for logic circuits whose functionality is to be checked.